Investments in Real Estate (Details)	12 Months Ended
	Dec. 31, 2018 NumberofUnits
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Number of Units	3,431
Whetstone Apartments [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Durham, NC
Number of Units	204
Actual Or Estimated Initial Occupancy	3Q 2014
Actual Or Estimated Construction Completion	3Q 2015
Alexan CityCentre [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Houston, TX
Number of Units	340
Actual Or Estimated Initial Occupancy	2Q 2017
Actual Or Estimated Construction Completion	4Q 2017
Helios [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Atlanta, GA
Number of Units	282
Actual Or Estimated Initial Occupancy	2Q 2017
Actual Or Estimated Construction Completion	4Q 2017
Alexan Southside Place [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Houston, TX
Number of Units	270
Actual Or Estimated Initial Occupancy	4Q 2017
Actual Or Estimated Construction Completion	1Q 2018
Leigh House, formerly Lake Boone Trail [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Raleigh, NC
Number of Units	245
Actual Or Estimated Initial Occupancy	3Q 2017
Actual Or Estimated Construction Completion	3Q 2018
Vickers Historic Roswell, formerly Vickers Village [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Roswell, GA
Number of Units	79
Actual Or Estimated Initial Occupancy	2Q 2018
Actual Or Estimated Construction Completion	3Q 2018
Domain at The One Forty, formerly Domain [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Garland, TX
Number of Units	299
Actual Or Estimated Initial Occupancy	2Q 2018
Actual Or Estimated Construction Completion	4Q 2018
Arlo, formerly West Morehead [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Charlotte, NC
Number of Units	286
Actual Or Estimated Initial Occupancy	2Q 2018
Actual Or Estimated Construction Completion	2Q 2019
Cade Boca Raton, formerly APOK Townhomes [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Boca Raton, FL
Number of Units	90
Actual Or Estimated Initial Occupancy	4Q 2018
Actual Or Estimated Construction Completion	2Q 2019
Novel Perimeter, formerly Crescent Perimeter [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Atlanta, GA
Number of Units	320
Actual Or Estimated Initial Occupancy	3Q 2018
Actual Or Estimated Construction Completion	2Q 2019
Flagler Village [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Fort Lauderdale, FL
Number of Units	385
Actual Or Estimated Initial Occupancy	2Q 2020
Actual Or Estimated Construction Completion	3Q 2020
North Creek Apartments [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Leander, TX
Number of Units	259
Actual Or Estimated Initial Occupancy	4Q 2019
Actual Or Estimated Construction Completion	3Q 2020
Riverside Apartments [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Austin, TX
Number of Units	222
Actual Or Estimated Initial Occupancy	3Q 2020
Actual Or Estimated Construction Completion	4Q 2020
Wayforth at Concord [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Concord, NC
Number of Units	150
Actual Or Estimated Initial Occupancy	1Q 2020
Actual Or Estimated Construction Completion	2Q 2021
Average [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Number of Units	11,286
ARIUM at Palmer Ranch [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Sarasota, FL
Number of Units	320
Date Built / Renovated	2016	[1]
Ownership Interest	100.00%
ARIUM Glenridge [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Atlanta, GA
Number of Units	480
Date Built / Renovated	1990	[1]
Ownership Interest	90.00%
ARIUM Grandewood [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Orlando, FL
Number of Units	306
Date Built / Renovated	2005	[1]
Ownership Interest	100.00%
ARIUM Gulfshore [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Naples, FL
Number of Units	368
Date Built / Renovated	2016	[1]
Ownership Interest	100.00%
ARIUM Hunter's Creek [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Orlando, FL
Number of Units	532
Date Built / Renovated	1999	[1]
Ownership Interest	100.00%
ARIUM Metrowest [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Orlando, FL
Number of Units	510
Date Built / Renovated	2001	[1]
Ownership Interest	100.00%
ARIUM Palms [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Orlando, FL
Number of Units	252
Date Built / Renovated	2008	[1]
Ownership Interest	100.00%
ARIUM Pine Lakes [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Port St. Lucie, FL
Number of Units	320
Date Built / Renovated	2003	[1]
Ownership Interest	85.00%
ARIUM Westside [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Atlanta, GA
Number of Units	336
Date Built / Renovated	2008	[1]
Ownership Interest	90.00%
Ashford Belmar [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Lakewood, CO
Number of Units	512
Date Built / Renovated	1988/1993	[1]
Ownership Interest	85.00%
Ashton Reserve [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Charlotte, NC
Number of Units	473
Date Built / Renovated	2015	[1]
Ownership Interest	100.00%
Citrus Tower [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Orlando, FL
Number of Units	336
Date Built / Renovated	2006	[1]
Ownership Interest	96.80%
Enders Place at Baldwin Park [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Orlando, FL
Number of Units	220
Date Built / Renovated	2003	[1]
Ownership Interest	92.00%
James on South First [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Austin, TX
Number of Units	250
Date Built / Renovated	2016	[1]
Ownership Interest	90.00%
Marquis at Crown Ridge [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	San Antonio, TX
Number of Units	352
Date Built / Renovated	2009	[1]
Ownership Interest	90.00%
Marquis at Stone Oak [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	San Antonio, TX
Number of Units	335
Date Built / Renovated	2007	[1]
Ownership Interest	90.00%
Marquis at The Cascades [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Tyler, TX
Number of Units	582
Date Built / Renovated	2009	[1]
Ownership Interest	90.00%
Marquis at TPC [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	San Antonio, TX
Number of Units	139
Date Built / Renovated	2008	[1]
Ownership Interest	90.00%
Outlook at Greystone [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Birmingham, AL
Number of Units	300
Date Built / Renovated	2007	[1]
Ownership Interest	100.00%
Park & Kingston [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Charlotte, NC
Number of Units	168
Date Built / Renovated	2015	[1]
Ownership Interest	100.00%
Plantation Park [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Lake Jackson, TX
Number of Units	238
Date Built / Renovated	2016	[1]
Ownership Interest	80.00%
Preston View [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Morrisville, NC
Number of Units	382
Date Built / Renovated	2000	[1]
Ownership Interest	100.00%
Roswell City Walk [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Roswell, GA
Number of Units	320
Date Built / Renovated	2015	[1]
Ownership Interest	98.00%
Sands Parc [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Daytona Beach, FL
Number of Units	264
Date Built / Renovated	2017	[1]
Ownership Interest	100.00%
Sorrel [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Frisco, TX
Number of Units	352
Date Built / Renovated	2015	[1]
Ownership Interest	95.00%
Sovereign [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Fort Worth, TX
Number of Units	322
Date Built / Renovated	2015	[1]
Ownership Interest	95.00%
The Brodie [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Austin, TX
Number of Units	324
Date Built / Renovated	2001	[1]
Ownership Interest	92.50%
The Links at Plum Creek [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Castle Rock, CO
Number of Units	264
Date Built / Renovated	2000	[1]
Ownership Interest	88.00%
The Mills [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Greenville, SC
Number of Units	304
Date Built / Renovated	2013	[1]
Ownership Interest	100.00%
The Preserve at Henderson Beach [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Destin, FL
Number of Units	340
Date Built / Renovated	2009	[1]
Ownership Interest	100.00%
Veranda at Centerfield [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Houston, TX
Number of Units	400
Date Built / Renovated	1999	[1]
Ownership Interest	93.00%
Villages at Cypress Creek [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Houston, TX
Number of Units	384
Date Built / Renovated	2001	[1]
Ownership Interest	80.00%
Wesley Village [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Charlotte, NC
Number of Units	301
Date Built / Renovated	2010	[1]
Ownership Interest	100.00%

[1] Represents date of last significant renovation or year built if there were no renovations.